introduction multimedia
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SMIL

 SMIL is pronounced as smile. SMIL, the Synchronized Multimedia Integration Language, has been inspired by the Amsterdam Hypermedia Model (AHM). In fact, the dutch research group at CWI that developed the AHM actively participated in the SMIL 1.0 committee. Moreover, they have started a commercial spinoff to create an editor for SMIL, based on the editor they developed for CMIF. The name of the editor is GRINS. Get it?

As indicated before SMIL is intended to be used for

SMIL


TV-like multimedia presentations

The SMIL language is an XML application, resembling HTML. SMIL presentations can be written using a simple text-editor or any of the more advanced tools, such as GRINS. There is a variety of SMIL players. The most wellknown perhaps is the RealNetworks G8 players, that allows for incorporating RealAudio and RealVideo in SMIL presentations.

parallel and sequential


Authoring a SMIL presentation comes down, basically, to

name media components for text, images,audio and video with URLs, and to schedule their presentation either in parallel or in sequence.

Quoting the SMIL 2.0 working draft, we can characterize the SMIL presentation characteristics as follows:

presentation characteristics


Where HTML has become successful as a means to write simple hypertext content, the SMIL language is meant to become a vehicle of choice for writing synchronized hypermedia. The working draft mentions a number of possible applications, for example a photoalbun with spoken comments, multimedia training courses, product demos with explanatory text, timed slide presentations, onlime music with controls.

applications


As an example, let's consider an interactive news bulletin, where you have a choice between viewing a weather report or listening to some story about, for example, the decline of another technology stock. Here is how that could be written in SMIL:

example



   <par>
      <a href="#Story"> <img src="button1.jpg"/> </a>
      <a href="#Weather"> <img src="button2.jpg"/></a>
       <excl>
           <par id="Story" begin="0s">
             <video src="video1.mpg"/>
             <text src="captions.html"/>
           </par>
  
           <par id="Weather">
             <img src="weather.jpg"/>
             <audio src="weather-rpt.mp3"/>
           </par>
       </excl>
   </par>
Notice that there are two parallel (PAR) tags, and one exclusive (EXCL) tag. The exclusive tag has been introduced in SMIL 2.0 to allow for making an exclusive choice,so that only one of the items can be selected at a particular time. The SMIL 2.0 working draft defines a number of elements and attributes to control presentation, synchronization and interactivity, extending the functionality of SMIL 1.0.

Before discussing how the functionality proposed in the SMIL 2.0working draft may be realized, we might reflect on how to position SMIL with respect to the many other approaches to provide multimedia on the web. As other approaches we may think of flash, dynamic HTML (using javascript), or java applets. In the SMIL 2.0 working draft we read the following comment:

history


Experience from both the CD-ROM community and from the Web multimedia community suggested that it would be beneficial to adopt a declarative format for expressing media synchronization on the Web as an alternative and complementary approach to scripting languages.

Following a workshop in October 1996, W3C established a first working group on synchronized multimedia in March 1997. This group focused on the design of a declarative language and the work gave rise to SMIL 1.0 becoming a W3C Recommendation in June 1998.

In summary, SMIL 2.0 proposes a declarative format to describe the temporal behavior of a multimedia presentation, associate hyperlinks with media objects, describe the form of the presentation on a screen, and specify interactivity in multimedia presentations. Now,why such a fuzz about "declarative format"? Isn't scripting more exciting? And aren't the tools more powerful? Ok, ok. I don't want to go into that right now. Let's just consider a declarative format to be more elegant. Ok?

To support the functionality proposed for SMIL 2.0 the working draft lists a number of modules that specify the interfaces for accessing the attributes of the various elements. SMIL 2.0 offers modules for animation, content control, layout, linking, media objects, meta information, timing and synchronization, and transition effects.

SMIL 2.0 Modules


  • The Animation Modules
  • The Content Control Modules
  • The Layout Modules
  • The Linking Modules
  • The Media Object Modules
  • The Metainformation Module
  • The Structure Module
  • The Timing and Synchronization Module
  • The Time Manipulations Module
  • The Transition Effects Module

This modular approach allows to reuse SMIL syntax and semantics in other XML-based languages, in particular those that need to represent timing and synchronization. For example:

module-based reuse


  • SMIL modules could be used to provide lightweight multimedia functionality on mobile phones, and to integrate timing into profiles such as the WAP forum's WML language, or XHTML Basic.
  • SMIL timing, content control, and media objects could be used to coordinate broadcast and Web content in an enhanced-TV application.
  • SMIL Animation is being used to integrate animation into W3C's Scalable Vector Graphics language (SVG).
  • Several SMIL modules are being considered as part of a textual representation for MPEG4.
The SMIL 2.0 working draft is at the moment of writing being finalized. It specifies a number of language profiles topromote the reuse of SMIL modules. It also improves on the accessibility features of SMIL 1.0, which allows for, for example,, replacing captions by audio descriptions.

In conclusion, SMIL 2.0 is an interesting standard, for a number of reasons. For one, SMIL 2.0 has solid theoretical underpinnings in a well-understood, partly formalized, hypermedia model (AHM). Secondly, it proposes interesting functionality, with which authors can make nice applications. In the third place, it specifies a high level declarative format, which is both expressive and flexible. And finally, it is an open standard (as opposed to proprietary standard). So everybody can join in and produce players for it!
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eliens@cs.vu.nl

draft version 1 (16/5/2003)